Golf requires a combination of physical skill and mental toughness. Accuracy is required for lower scores. "Feel" is also a significant part of the game. The golfer analyzes the feedback or sensations after each shot to make necessary adjustments for mis-hits or to add consistency to his swing.
Studies show that the initiation of the downswing excites a torsional and bending impulse in the shaft which causes the clubhead to rotate from the optimal "square" position. Independent tests using a mechanical swing robot show that shot dispersion for a 220 yard drive averages approximately .+-.38 feet due to this head rotation. Regardless of the consistency of the swing, or the similarities of golf balls, a golfer's accuracy is at the mercy of his/her equipment.
It is also known that the impact of the clubhead on the golfball excites a vibratory phenomena through the shaft which propagates into the golfer's hands and arms. Not only do these vibrations cause fatigue, they also play into the golfer's subconscious, as he/she adjusts his/her grip, his/her stance, or his/her swing in anticipation of this unpleasant sensation prior to each subsequent shot.
The golf shaft has an infinite number of vibratory mode shapes. Independent studies show that vibrations in a golf club are most readily detected at frequencies up to 750 Hertz. This value falls within the first four modes of a composite golf shaft. Thus, vibration damping is significant up to the fourth mode.
Conventionally, there have been a number of ways to incorporate damping into golf shaft design. Current techniques call for the placement of foam or rubber inserts into the bore of the shaft. Another design utilizes the theory of Constrained Layer Damping (CLD), where a viscoelastic adhesive is attached to the surface of a shaft by means of a rigid, constraining layer; see, e.g., U.S. Pat. No. 5,294,119, issued to Benoit Vincent et al on Mar. 15, 1994.
Each of these conventional designs has drawbacks. By adding a distinct damping device to an existing shaft, each of these designs adds weight to the completed club. All designs require the shaft to be the primary structural member. Finally, these designs only control damping when the shaft undergoes out-of-plane vibrations.
What is needed is a means of damping a golf shaft which avoids most, if not all, of the foregoing drawbacks.